Marking or embedding printed articles such as documents, images, packaging, and so on, with machine-readable information has a variety of applications, including document identification and authentication, copy prevention, counterfeit prevention, copyright protection, document organization, and so on. Example forms that are often used to embed machine-readable information into printed articles include watermarks and barcodes. More recently, embedded machine-readable information is being used as a way to link additional, related content to printed articles. For example, in mobile tagging, a barcode printed on a document or image can be scanned by a smartphone in order to link the smartphone user to a related online digital experience (e.g., a video, additional documents and images, etc.). Instead of using the conventional black and white “line” barcode, this tagging method typically uses a more sophisticated two-dimensional barcode, such as a QR (quick response) Code or a tag barcode that can incorporate full-color custom images, such as a company logo.
Barcodes and other prior methods of encoding data are generally effective in providing machine-readable information on printed documents. Some methods enable the information to be hidden or otherwise unnoticeable to a user, while in other methods the information is readily perceivable and sometimes even comprehendible by the user. In general, prior methods of embedding machine-readable information in a document usually involve either altering the document content (e.g., altering an image) to hide the information, or using at least some surface area of the document that could otherwise be used for text or other images.